20110930024519A

Glassair iii experimental aircraft was modified on 10/21/2010 to remove the Lycoming IO-540 engine and install a chevrolet corvette lsi engine with an aluminum redrive case and 1.667 gear reduction / clutch system. FAA records indicate that a letter was issued by the FAA authorizing the aircrat to re-enter phase 1 testing on 10/26/2010 and later rescinded on 11/19/2010. FAA records do not indicate authorization was later obtained for phase 1 testing, due to the engine change, as required in the operations limitations for the aircrft. On 09/30/2011, pilot departed 2I3 from the downwind runway with no apparent run-up checks. Pilot performed 2 low level, high speed passes with airshow type turns at the ends. Witnesses indicate hearing the engine begin to surge at the end of the first pass. With high engine power, aircraft descended into the back of a hotel building and exploded. On-scene investigation revealed loose propeller main bearing. Vast quantities of aluminum shavings were found in the redrive housing and main propeller shaft was sheared. Counterweights on the clutch / flywheel were all missing. NTSB laboratory is working to determine failure mode of main bearing, shaft and counterweight assembly.